Consider a circuit such as a computer memory that is constructed from layers of planar arrays of memory cells that are stacked to form a 3-dimensional memory. The layers may be individual integrated circuit chips or traditional circuit boards. The layers are typically connected by a number of vertical connect lines. Typically, there is an address associated with each layer and an enablement line that connects that layer to one or more of the vertical connect lines when the cells thereon are being selected.
There are two basic methods for selecting a layer. In the first method, the address of the selected layer can be communicated on a subset of the vertical connect lines and be decoded on the layer. The decoded address is then compared to an address stored on the layer, and if the addresses match, the enablement line is energized. This method requires that each layer be programmed with its specific address prior to being connected in the stack. Hence, the layers are not identical. In addition, the ROM needed to store the address may require a different fabrication technology than the remaining circuitry on the layer. This is particularly important in the cases in which the layers are individual semiconductor chips, since mixing devices constructed with different fabrication processes is not always possible.
The second method places the decoding circuitry on a different layer. In this case, each layer must have an enablement connection in the vertical connect lines. The vertical connected select lines must be distinct and each layer must "know" which line corresponds to that layer while being identical to every other layer. No prior art solution to this problem is known that does not require programming bits on each layer to make that layer unique.
Broadly, it is the object of the present invention to provide an improved layer select arrangement in a circuit constructed from a plurality of identical circuit layers.
It is a further object of the present invention to provide a layer select method that does not require each layer to be separately programmed with an address.
These and other objects of the present invention will become apparent to those skilled in the art from the following detailed description of the invention and the accompanying drawings.